When considering the interface between a normal metal (NM) and a magnetic material (here considered
a ferromagnetic insulator, FMI) in a junction, two processes deserve special attention.
The first one is related to the spin current injection from the conductor to the magnetic side due to the spin accumulation
on the normal metal close to the interface, termed Spin-Transfer Torque (SST) [1]}, [2]}. Then, in this case, the angular
momentum injection can induce the magnetization to precess around the ordered axis or even revert its orientation.
On the other hand, the opposite process, named Spin
Pumping (SP), involves the injection of pure spin current from the magnetic side to the conductor [3]}. The SP process can be
provided by Ferromagnetic Resonance (FMR) or Electron Paramagnetic Resonance (EPR), depending on the magnetic sample [4]}.
In both processes, a resonant magnetic field induces the magnetization to precess and emit angular momentum that is propagated via spin
waves. In addition, due to the magnon absorption, conduction electrons close to the interface are scattered through a spin-flip process.
The EPR/FMR-driven spin pumping is frequently detected on the conductor side by using a metal with strong spin-orbit coupling. Therefore,
due to the Inverse Spin Hall Effect (ISHE) [5]}, [6]}, the spin current injected is converted into a charge current that
provides a d.c. Voltage on the metal. A detailed explanation of SST and SP processes can be found in Ref. [7]}, [8]}.
